I have a 89 wrangler 4 cyl 2.5L. I bought a rebuilt AX-15 transmission from a jeep mechanic in the area. I put the tranny in to find that it wont shift out of first gear while driving. It shifts fine while motor is not running. when driving in first gear I go to change to second and it grinds, also while starting off in first I can hear a slight rattle from under the jeep. I didn't replace the clutch or anything else.

Did you bleed the clutch? If not start there, if so it could be time to change the slave, the throwout bearing would have to be really bad to not get out of first. I've only had the throwout make noise, not keep it from shifting.

The 2.5 doesn't bolt up directly to an AX-15... what sort of adapter did you use?

As far as my research has taken me, there is no adapter for the 2.5 to anything, and nothing to adapt the ax5 to any other engine. Im thinking he got a bad ax5, take it to your trans re builder and have him give his opinion, he is the best guy to advise you IF HE IS HONEST.....

There is away to bolt up ax-15 to a 2.5l. We did it on my friends yj not sure on all the parts he gathered them up. Had something to do with a 96 dodge truck with a 4cyl. Now to your problem how's the fluid?

Have you tried to power shift up by just letting off the gas and easing shifter into next gear without even pushing the clutch in? If that works syncros are pretty good and you need to think about the clutch setup.